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Developing Ultra Small-Scale Radiocarbon Sample Measurement at the University of Tokyo

Published online by Cambridge University Press:  18 July 2016

Yusuke Yokoyama ,
Mamito Koizumi ,
Hiroyuki Matsuzaki ,
Yosuke Miyairi  and
Naohiko Ohkouchi
Yusuke Yokoyama*
Affiliation:
Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Chiba 277-8564, Japan Department of Earth and Planetary Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyoku, Tokyo 113-0033, Japan Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan
Mamito Koizumi
Affiliation:
Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Chiba 277-8564, Japan Department of Earth and Planetary Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyoku, Tokyo 113-0033, Japan
Hiroyuki Matsuzaki
Affiliation:
Department of Nuclear Engineering and Management, University of Tokyo, Tokyo, Japan
Yosuke Miyairi
Affiliation:
Department of Nuclear Engineering and Management, University of Tokyo, Tokyo, Japan
Naohiko Ohkouchi
Affiliation:
Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan
*
Corresponding author: Email: yokoyama@ori.u-tokyo.ac.jp
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Abstract

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We have developed accelerator mass spectrometry (AMS) measurement techniques for ultra small-size samples ranging from 0.01 to 0.10 mg C with a new type of MC-SNICS ion source system. We can generate 4 times higher ion beam current intensity for ultra-small samples by optimization of graphite position in the target holder with the new ionizer geometry. CO2 gas graphitized in the newly developed vacuum line is pressed to a depth of 1.5 mm from the front of the target holder. This is much deeper than the previous position at 0.35 mm depth. We measured 12C4+ beam currents generated by small standards and ion beam currents (15–30 μA) from the targets in optimized position, lasting 20 min for 0.01 mg C and 65 min for 0.10 mg C. We observed that the measured 14C/12C ratios are unaffected by the difference of ion beam currents ranging from 5 to 30 μA, enabling measurement of ultra-small samples with high precision. Examination of the background samples revealed 1.1 μg of modern and 1 μg of dead carbon contaminations during target graphite preparation. We make corrections for the contamination from both the modern and background components. Reduction of the contamination is necessary for conducting more accurate measurement.

Type
Accelerator Mass Spectrometry
Information
Radiocarbon , Volume 52 , Issue 2: 20th Int. Radiocarbon Conference Proceedings , 2010 , pp. 310 - 318
Copyright
Copyright © 2010 by the Arizona Board of Regents on behalf of the University of Arizona 

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